What is the definition of an isogonal?

An isogonal is defined as a line connecting points of equal variation. In the context of aeronautical navigation, variation refers to the difference between magnetic north and true north, measured in degrees. Isogonals are significant for pilots as they provide crucial information about the magnetic variation in different geographical areas, which is essential for accurate navigation. Understanding these lines helps ensure that the aircraft's heading aligns correctly with its intended course.

The other options relate to meteorological and altimetry concepts but do not define isogonals. Weather fronts indicate boundary areas between different air masses, temperature lines (isotherms) connect points of equal temperature, and pressure altitudes pertain to atmospheric pressure measurement. Each of these has its own defined applications and significance in aviation, but they do not pertain to the concept of variation in navigation.